Organo-siloxanes and methods of preparing them



was Apr. z, 1946 ORGANO-SILOXANES AND METHODS OF PREPARING THEM EarlLeathen Wan'lck, Pittsburgh, Pa., assignmto Corning Glass Works,Corning, N. Y., a corporation of New York No Drawing. ApplicationFebruary 14, 1945,

Serial No. 577,936

8 Claims.

This invention relates to methyl siloxanes and methods of preparingthem.

Methyl siloxanes are compositions comprising essentially silicon atomsconnected to each other by oxygen atoms through silicon-oxygen linkages,

and methyl radicals attached through carbonsilicon linkages to at leastsome of the silicon atoms. They may be prepared by the hydrolysis of ahydrolyzable mono-, di-, or tri-xnethyl substituted monosilane followedby condensation (partial or complete) of the hydrolysis product.

' By employing such mixtures of silanes, it ispossible to prepare methylsiloxanes which contain on the average between zero and three methylradicals per silicon atom. Y

The products resulting from the hydrolysis and condensation ofhydrolyzable methyl silanes or mixtures thereof differ considerably withrespect to their ability to retain their physical properties.

at elevated temperatures. In general, the liquids become more viscousand lose weight when held at high temperatures for extended periods oftime. Likewise the solids undergo loss in weight and tend to crack whensubjected to high temperatures for prolonged periods. For manyindustrial applications, it is important that these products remainsubstantially unchanged when exposed to high temperatures tor a longtime. For example, as hydraulic fluids, they should not lose weight norincrease appreciably in viscosity. As solid insulating coatings formetallic conductors, they should not lose weight and crack.

' It has been found that the thermal stability of the methyl siloxanesis greatly enhanced if they contain trimethyl silicyl units.v Theincorporation of the latter into the methyl siloxanes producescompositions which are relatively resistant to elevated temperatures forprolonged periods. A method of preparing such methyl siloxanes isdescribed in the. coperiding application of James Franklin Hyde, SerialNumber 432,528, filed February 26, 1942. This method compriseshydrolyzing a mixture oi silanes containing a hydrolyzabletri-methyl-substituted silane and inter-condensing the hydrolysisproducts. Although this method makes it possible to produce methylsiloxanes which represent a great improvement over the art, it possessesthe objectionable feature that when sumclent trimethyl-silicyl units areintroduced to effect the desired increase in stability-,- the resultingproduct in many instances is a liquid which has too low a viscosity.Furthermore, there are many applications which require materials of aneven greater stability than this method can provide. Accordingly, "it isan object of this invention to provide a method of preparing methylsiloxanes which possess a greater heat resistance and a higher viscositythan methyl slloxanes previously prepared and yet having substantiallythe same chemical composition.

Another object of my invention is to prepare new compositions of mattercomprising methyl siloxanes of greatly improved resistance to change atelevated temperatures.

Other objects and advantages will be apparent from the followingdescription.

In accordance with my invention, I have provided a method or preparingheat resistant methyl siloxanes which comprises interacting a partiallycondensed siloxane having on the average up to 2.5 methyl radicalsattached to each silicon atom through carbon-silicon linkages withtrimethylethoxysilane in the presence of water. I have found that bythis method methyl siloxanes may be prepared which are much more stableand more viscous than methyl siloxanes of the same average number ofmethyl radicals per slliconatom and which were prepared by concurrentlyhydrolyzing and condensing the trimethylethoxysilane and the othercomponents of the methyl siloxane. The reason for this is not definitelyestablished, but the increased stability of the product is quiteimpressive as will be clearly apparent from the examples given below. i

In general, the preferred method of practicing my invention is asfollows. An ethoxysilane having from 1 to 2 methyl radicals per siliconatom, either alone or in a mixture of ethoxysilanes containing on theaverage up to 2.5 methyl radicals per silicon atom, is first hydrolyzedby excess water under conditions which promote only partial condensationof the hydrolysis product. The following conditions aid in obtainingonly partial condensation. The reaction should be carried out in a watermiscible solvent and preferably in a dilute solution. The reactiontemperature should be kept down since heat promotes dehydration andconsequent condensation. To the reaction mixture is then addedtrimethylethoxy- Example 1 A mixture consisting of 90 parts by weight ofethyldiethoxysilane and 10 parts by weight of methyltriethsilane wasrefluxed for four hours with an equal volume of 1:1 alcohol and hy=drochloric acid mixture. The latter mixture contained more than sumcientwater to completely hydrolyze the silanes. .At the conclusion of therefluxing, 10 parts by weight of trimethylethxysilene was added dropwiseto the mixture. Refiualng was continued for one hour. The product waswashed and low polymers removed by distillation up to a temperature of230 C. The viscosity of the product was 45.5 centistokes at 25 C.

when a trimethylethoxysilane was added to the mixture ofmethyltriethoxysllane and dimethyldiethoxysilane prior to hydrolysis andthe resulting mixture treated in the same manner as above, a producthaving a viscosity of 21.9 centistokes was obtained The two productswere heated to 200" C. and held there until gelation occurred. Theproduct obtained by concurrently hydrolyzing and condensing the mixtureof the three components gelled in 63 hours. On the other hand, theproduct obtained by first hydrolyzing the mixture of 7 two componentsand then adding the third component gelled only after 256 hours ofheating at 200 C.

,E ample 2 A mixture consisting of 75 parts by weight ofdimethyldiethoxysilane and 25 parts by weight of methyltriethoxysilanewas refluxed for four hours with an equal volume of 1:1 ethyl alcoholand hydrochloric acid mixture. At the conclusion of the refluxing, 25parts by weight of trimethylethoxysilane were added dropwise to themixture. Refluxing was continued for one hour. The product was washedand low polymers removed by distillation up to a temperature of 230 C.The viscosity of the product was 55.0 centistokes at 25 C.

When the trimethylethoxysilane was added to the mixture ofmethyltriethoxysilane and dimethyldiethoxysilane prior to hydrolysis andthe resulting mixture treated in accordance with the procedure outlinedabove, a product having a viscosity of 14.5 centistokes was obtained.

The two products were heated to 200 C. and held there until gelationoccurred. The product obtained by hydrolyzing the mixture of the threecomponents gelled in 94 hours; whereas the product obtained by firsthydrolyzing the mixture of two components and then adding the thirdcomponent gelled only after 186 hours at 200 C.

Example 3 Ninety parts by weight of dimethyldiethoxysilone washydrolyzed by adding twice the theoretical amount of water required and3 per cent by weight of sulphuric acid based on the ester. The mixturewas immediately stirred and distilled to 100 C. Following this 10partsby weight of trimethylethoxysilane was added 'dropwise through a.vertical condenser. The mixture was stirred at 100 C. for one hour,followed by washing and removal of low polymers by distillation up to atemperature of 230, C. The product had a viscosity of 30 centlstohes at25 C.

When the trimethylethoxysilane wa added to the dimethyldiethoxysllanebefore lwdrolysis, the product obtained by the above treatment hadviscosity of 11.9 centistokes.

The two products wer heated to 200 C. and held there until gelationoccurred. The product obtained by hydrolyzing the mixture oitwocomponents gelled in 276 hours; while the product obtained byhydrolyzing first one component and then adding the other componentgelled only after 708 hours at 200 C.

, Example 4 Seventy-five parts by weight of dimethyldiethoxysilane washydrolyzed by adding twice the theoretical amount of water required and3 per cent by weight of sulphuric acid based on the ester. The mixturewas immediately stirred and distilled to 100 C. Following this 25 partsby weight of trimethylethoxysilane were added dropwise through avertical condenser. The mixture was stirred at 100 C. for one hour,followed by washing and removal of low polymers by distillatreatment hada viscosity of 5.4 centistokes.

The two products were heated to 200 C. and

* held ther until, gelation' occurred. The product obtained byhydrolyzing the mixture of two componcnts gelled in approximately 250hours; while the product obtainedb hydrolyzing first the one componentand then adding the other compogg t gelled only after approximately 700hours at Example 5 A mixture of mol per cent of methyltriethoxysilaneand 15 mol per cent of trimethylvethoxysilane was dropped into an equalvolume of 2 N hydrochloric acid at such a rate that the temperature didnot rise above 40 C. The mixture was then heated at 60 C, for one hour.Ten mol percent of trimethylethoxysilane was then added. The resultingmixture was heated for another hour at 60 C. The product was then washedwith water; dissolved in xylene and dried by refluxing in a systemcontaining a water trap. The solvent was removed leaving a liquid of18,000 centistokes viscosity. This liquid was heated 5 hours at C.losing 26.1% of its weight and being converted to a. solid resin in theprocess. Further heating at 250 C. for 16 hours, however, resulted inonly 1.8% loss in weight.

When all the trimethylethoxysilane wasadded initially to the mixture,and hydrolyzed by the above technique, a. liquid product of only 300centistokes viscosity was produced. This lost 34.6% of its weight whenheated for 5 hours at 150 0., being converted to a resinous solid in theprocess and 15% more of its weight when heated 16 hours at 250 C. ascontrasted with the 1.8% in the case of the above-described liquid.Prior to' heating at 150 C. both products had a. carbon to silicon ratioof 1.45. Further evidence that the two products, although ofsubstantially the same chemical composition. were structurally differentwas the difierence in' their solubility in alcohol. The product havingthe viscosity of 18,000 centistokes lest only 4% by weight whenextracted once with 5 times its weight of alcohol while the liquid of300 centistokes viscosity dissolved completely.

The products of my invention which remain liquid even at elevatedtemperatures are useful in hydraulic pressure systems or as liquidfilling medium for transformers, circuit breakers, submarine cables,condensers, etc. The solid products are useful as molding compounds,film iorming coatings, varnishes, impregnating agents for electricalinsulation and the like.

I claim:

1. hi the method of preparing new synthetic compositions from apartially condensed methyl siloxane having on the average up to about2.5

methyl radicals per silicon atom, the step comthe composition consistsof dimethyldiethoxysil- 3. The method according to claim 2 wherein thecomposition consists of dimethyidiethoxysilane. 4. The method accordingto claim 2 wherein ane and methyltriethoxysilane.

5. The method according to claim 2 wherein the composition consists ofmethyltriethoxysilane and trimethylethoxysilane.

v in the presence of a hydrolysis catalyst, where n is an integer from 1to 2, partially condensing the hydrolysis-product, addingtrimethylethoxysilane to the mixture, and then continuing thecondensation to substantial completion.

7. The method which comprises reacting dimethyldiethoxysilane withexcess water in the presence of sulfuric acid, addingtrimethylethoxysilane to the reaction product, dehydrating the resultingmixture, and then recovering the resulting methyl silicon copolymer.

8. The method which comprises reacting dimethyldiethoxysilane withexcess water in the presence of sulfuric acid, distilling the reactionproduct to remove that part boiling below 0., addingtrimethylethoxysilane to the residual reaction product, heating theresulting mixture at about 100 C. for at least one hour, washing theproduct, and distilling of! the volatile components boiling below about230 C.

EARL LEATHEN WARRICK.

